Calcium cost/availability

The sustained world popularity of NSP results from simplicity of production and high agronomic quaHty as a carrier of available P2O5, calcium, sulfur, and usually some incidental micronutrients. In terms of agronomic value for large numbers of crops, no phosphate fertilizer has been shown to be superior to NSP. It is likely to remain in strong demand in parts of the world where simplicity of production or sulfur fertilization has high priority and where transportation costs are not prohibitive. 

The use of cesium fluoride is limited because of its cost and its availability as a truly anhydrous reagent. Its use with 18-crown-6 shows a 5 times higher rate for the formation of benzyl fluoride from benzyl bromide when compared with cesium fluonde or potassium fluoride supported on calcium fluoride [21] Either cesium fluoride or potassium fluoride supported on calcium fluoride (Procedures 5a and 5b, p 194) provides about a twofold improvement over either unsupported alkali metal fluoride [55, 69], Cesium fluoride and Aliquat 336 convert benzyl bromide to the fluoride in 94% yield. Using tetrabuty lammonium fluoride in place of Aliquat... 

Most of the forementioned studies which examined the influence of various dietary fiber on the bioavailability of calcium by human subjects have depended upon the comparative measurements of calcium content of diets and calcium contents of stools and urine. As reviewed by Allen (3), calcium balance studies have distinct limitations relative to accuracy and precision. However, their ease of application and cost, laboratory equipment requirements, and real (or perceived) safety in comparison to available radioactive or stable isotope methods continue to make their use popular. In calcium balance studies, calcium absorption is assumed to be the difference between calcium excretion in the feces and calcium intake. Usually this is expressed as a percent of the calcium intake. This method assumes that all fecal calcium loss is unabsorbed dietary calcium which is, of course, untrue since appreciable amounts of calcium from the body are lost via the intestinal route through the biliary tract. Hence, calcium absorption by this method may underestimate absorption of dietary calcium but is useful for comparative purposes. It has been estimated that bile salts may contribute about 100 g calcium/day to the intestinal calcium contents. Bile salt calcium has been found to be more efficiently absorbed through the intestinal mucosa than is dietary calcium (20) but less so by other investigators (21). 

Sulfur Emissicms Sulfur present in a fuel is released as SO2, a known contributor to acid rain deposition. By adding limestone or dolomite to a fluidized bed, much of this can be captured as calcium sulfate, a dry nonhazardous solid. As limestone usually contains over 40 percent calcium, compared to only 20 percent in dolomite, it is the preferred sorbent, resulting in lower transportation costs for the raw mineral and the resulting ash product. Moreover, the high magnesium content of the dolomite makes the ash unsuitable for some building applications and so reduces its potential for utilization. Whatever sorbent is selected, for economic reasons it is usually from a source local to the FBC plant. If more than one sorbent is available, plant trials are needed to determine the one most suitable, as results from laboratory-scale reactivity assessments are unreliable. 

Dolomite is an alternative mineral that is used in some regions in place of cal-cite for certain applications. Dolomite is a calcium magnesium carbonate (CaCOj.MgCOj) and occurs widely in nature. Although generally similar to cal-cite in properties, it is shghtly harder (3.5), denser (2.85) and more acid resistant. Production is similar to that for calcite,but miUing is more costly and it tends to only be available at the coarser end of the size spectrum. 

The choice of selected raw materials is very wide, but they must provide calcium oxide (lime), iron oxide [1309-37-1/, silica, and aluminum oxide (alumina). Examples of the calcereous (calcium oxide) sources are calcium carbonate minerals (aragonite [14791-73-2]y calcite [13397-26-7]> limestone [1317-65-3]y or marl), seashells, or shale. Examples of argillaceous (silica and alumina) sources are clays, fly ash, marl, shale, and sand. The iron oxide commonly comes from iron ore, days, or mill scale. Some raw materials supply more than one ingredient, and the mixture of raw materials is a function of their chemical composition, as determined by cost and availability. 

June 1971. In Norway, also because of low-cost hydroelectric energy once available, production of calcium nilritle by way of first producing nitric acid Was pioneered. 

Over the last few years, as powerful but relatively low-cost personal computers have become widely available, new indices and models have been proposed that use complex computer programs and often a different starting point than that of LSI to more accurately predict the formation of calcium carbonate and many other common types of scale, as well as calcium carbonate in combination with these scale types (as tends to happen in real life). 

The standard disinfectant for many of the world s potable drinking water supply systems (ozone and others are also widely used) and the product of choice for large cooling systems, usually available as a gas for lowest cost, but can be provided by liquids such as sodium hypochlorite (bleach) or solids such as calcium hypochlorite or isocyanurates. Any process contaminant leak tends to increase the chlorine demand, requiring additional chlorine to maintain disinfection rate. Poor penetrant of biomass and significantly reduced efficiencies over pH 8.0. 

This method is extremely sensitive to pH changes which can lead to inconsistent transfection efficiencies, especially when using homebrew transfection buffers. To some extent, this sensitivity can be limited by the use of commercially available kits containing chemicals and buffers that have undergone quality control procedures, ensuring better reproducibility of results and less lot-to-lot variation. Although the costs per transfection for this method are unrivaled, the attractiveness of calcium phosphate precipitation has declined over the past 15 years, partly due to the trickiness of the method itself, the limited transfection efficiencies, and the narrow cell spectrum for which it is suitable, and partly because more modem and efficient DNA delivery methods have emerged. 

Dihydrotachysterol, an analog of l,25(OH)2D, is also available for clinical use, though it is used much less frequently than calcitriol. Dihydrotachysterol appears to be as effective as calcitriol, differing principally in its time course of action calcitriol increases serum calcium in 1-2 days, whereas dihydrotachysterol requires 1-2 weeks. For an equipotent dose (0.2 mg dihydrotachy-sterol versus 0.5 ug calcitriol), dihydrotachysterol costs about one fourth as much as calcitriol. A disadvantage of dihydrotachysterol is the inability to measure it in serum. Neither dihydrotachysterol nor calcitriol corrects the osteomalacic component of renal osteodystrophy in the majority of patients, and neither should be used in patients with hypercalcemia, especially if the bone disease is primarily osteomalacic. 

The sulfur sorbent that has received the most attention is limestone because of its widespread availability and low cost. Unfortunately the conversion of limestone to calcium sulfate results in a volumetric increase, and it can be readily shown (8 ) that for particles that do not permit volumetric expansion on reaction the maximum conversion attainable is about 59 percent (the value is dependent on the specific volumes of reactant and product). This constraint can be avoided by use of dolomite, since the MgO is not sulfated and the void volume produced by the decomposition of MgCO and CaCO is sufficient to permit complete calcium utilization, but at the expense of an added weight of sorbent and added energy requirement for calcination. The above conclusions follow from consideration of the stoichiometric relations ... 

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